RU2322531C2 - Steel and tools for cold metalworking - Google Patents

Abstract

FIELD: metallurgy; making steels for cold metalworking.

SUBSTANCE: proposed steel contains the following constituents, mass-%: C, 0.60-0.85; (Si+Al),from trace amount to 0.3; Mn, 0.1-2.0; Cr, 4.5-5.5; Mo, 1.5-2.6; W, 1.0 max.; V, 0.42-0.65; Nb, Ti and Zr, 0.1 max. each; the remainder being iron and unavoidable admixtures. Steel contains in essence no primary carbides and possesses after hardening and high-temperature tempering at temperature of 500-600°C harness ranging from Rockwell C 57 to 63. Steel possesses high mechanical properties. Tools made from this steel have constant sizes at heat treatment, high fatigue durability and good machinability.

EFFECT: enhanced durability and machinability.

31 cl, 7 dwg, 7 tbl

Description

Technical field

The invention relates to steel for cold working, i.e. to steel intended for use in the case of processing materials in their cold state. Punches and dies for cold stamping and other tools for cold pressing, tools for cold extrusion and thread rolling dies, as well as cutting tools, such as knives, such as separating knives for cutting strips, circular knives and the like, are typical examples of the use of such steel . The invention also relates to the use of steel for the production of tools used in cold working, as well as to tools made from this steel.

BACKGROUND OF THE INVENTION

The aim of the invention is steel for cold working, which can be used, inter alia, for the above applications and which, therefore, should have the following properties:

- good ductility / impact strength;

- good hardenability, allowing through hardening in relation to traditional hardening in a vacuum furnace of products with a thickness of at least 300 mm;

- corresponding hardness, at least 60 Rockwell C hardness, after quenching and high temperature tempering, which gives high resistance to plastic deformation and, as for at least some steel applications, also corresponding wear resistance in the absence of nitriding or coating of the surface with titanium carbide and / or titanium nitride, or the like, for example, by chemical vapor deposition or vapor deposition coating techniques;

- good tempering resistance to allow nitriding or coating of the surface with titanium carbide and / or titanium nitride, or the like, for example, using any of these methods without reducing the hardness of the material in the case of applications that require a particularly high wear resistance of the tool.

Other important product features are:

- good dimensional stability during heat treatment;

- high fatigue life;

- good grindability, machinability, electric spark machinability and polishability.

More precisely, the aim of the invention is steel for dies, which can be used for the above applications, i.e. such steel, which essentially does not contain primary carbides and which under service conditions has a base consisting of tempering martensite.

Disclosure of invention

The above objectives and features can be realized by means of steel, the distinguishing features of which are set forth in the attached claims.

As for the individual elements of this steel alloy and their mutual influence, it is really stated below.

As indicated above, the steel according to the invention should not contain primary carbides, or contain only an extremely low amount thereof, i.e. steel should essentially be free of primary carbides, but nevertheless have a wear resistance acceptable for most of its applications. This can be achieved by using adequate hardness in the range of 57-63 on the Rockwell scale C, preferably hardness from 60 to 62 on the Rockwell scale C, under conditions of hardening and high-temperature tempering of steel, and the steel should have good toughness. To achieve this, steel contains carbon and vanadium in well-balanced amounts. Thus, the steel contains at least 0.60%, preferably at least 0.63%, and more preferably at least 0.68% C. Additionally, the steel should contain at least 0.30%, preferably at least 0, 35% and more preferably at least 0.42% V. This allows the steel in the quenched and tempered state to contain in the martensitic base sufficient carbon in the solid state to impart the specified hardness to the base, and also allows an adequate amount of secondary precipitation to form in the steel base ouch n small, increasing the hardness of vanadium carbides. In addition, very small primary precipitated vanadium carbides are present in steel, which contributes to the prevention of grain growth during heat treatment. Any carbides other than vanadium carbides should not exist. To realize these conditions, the steel should not contain more than 0.85%, preferably contain a maximum of 0.80%, more preferably a maximum of 0.78% C, and the amount of vanadium can reach a maximum of 0.65%, preferably a maximum of 0.60% or more preferably a maximum of 0.55%. Nominally, the steel contains 0.72% C and 0.50% V. The carbon content of the solid solution in the quenched and subjected to high temperature tempering steel is nominally approximately 0.67%.

Silicon is present, at least in measurable quantities, in the form of an element residual from steel production, and its amount is from trace amounts to 1.5%. Silicon, however, lowers the toughness of steel and, therefore, should not be present in an amount of more than 1.0%, preferably a maximum of 0.5%. Typically, silicon is present in a minimum amount of at least 0.05%. The effect of silicon is to increase the activity of carbon in steel and thus contributes to giving the steel the required hardness. Another positive effect of silicon is that it can improve the workability of steel. Thus, an advantage may be the silicon content in the steel in an amount of at least 0.1%. Nominally, steel contains 0.2% silicon.

To some extent, aluminum can have the same or similar effect as silicon, at least in the case of this type of steel. Both elements in the production of steel can be used as oxidation agents. Both of them are ferrite-forming elements and can provide the dissolution hardening effect at the base of steel. Thus, silicon can be partially replaced by aluminum up to a maximum amount of 1.0%. The aluminum in the steel, however, necessitates a very good deoxidation of the steel and a very low nitrogen content, since otherwise aluminum oxides and aluminum nitrides will form, which will significantly reduce the ductility / toughness of the steel. Thus, the steel should not usually contain more than a maximum of 1.0% Al, preferably a maximum of 0.3%. In a preferred embodiment of the invention, the steel contains a maximum of 0.1% and most preferably a maximum of 0.03% Al.

Manganese, chromium and molybdenum must be present in the steel in quantities sufficient to give the steel adequate hardenability. Manganese also has the property of binding extremely low amounts of sulfur, which may be present in steel, to form manganese sulfides. Thus, the manganese content should be 0.1-2.0%, preferably 0.2-1.5%. More preferably, the steel contains at least 0.25%, but a maximum of 1.0% manganese. The nominal amount of manganese is 0.50%.

To impart the required hardenability to steel, chromium must be present in an amount of at least 3.0%, preferably at least 4.0%, and more preferably at least 4.5%, if the steel contains manganese and chromium in amounts typical of steel. The maximum steel may contain 7.0%, preferably a maximum of 6.0% and more preferably a maximum of 5.5% chromium.

To give the steel the required hardenability, and also to give the steel the required secondary hardening, together with chromium, which is in the first place, molybdenum must also be present in the steel in an adequate amount. Too much molybdenum, however, promotes the precipitation of M6C carbides, which should preferably be absent in steel. Because of this, the steel should preferably contain at least 1.5%, but a maximum of 4.0% molybdenum. Preferably, the steel contains at least 1.8%, but a maximum of 3.2% molybdenum, more preferably at least 2.1%, but a maximum of 2.6% Mo, otherwise the steel will contain undesired M6C carbides instead and / or in addition to the right amount of MS carbides. In principle, to achieve the required hardenability, molybdenum can be partially or completely replaced with tungsten, but it requires twice as much as molybdenum, which is a significant drawback. In addition, the processing of any scrap obtained in connection with the production of steel is time consuming if the steel contains significant amounts of tungsten. Therefore, tungsten should not be present in steel in an amount of more than a maximum of 1.0%, preferably a maximum of 0.3%, more preferably a maximum of 0.1%. It is best that the steel does not contain specially added tungsten at all, which, in accordance with the most preferred embodiment of the present invention, can be present in steel only as an impurity, in the form of a residual element that enters with the raw materials used for the manufacture of steel.

In addition to these elements, it is usually not required that the steel contain any additional intentionally added alloying elements. For example, cobalt is an element that is usually not required to achieve the required properties by steel. However, cobalt may be present in an amount of maximum 2.0%, preferably maximum 0.7%, to further increase tempering resistance. However, usually steel contains cobalt in an amount not exceeding the impurity level. Nickel is another element whose presence in steel is not necessary, but which may possibly be present in it to increase the ductility of steel. However, with too much nickel, there is a risk of residual austenite formation. Thus, the nickel content should not exceed a maximum of 2.0%, preferably a maximum of 1.0%, more preferably a maximum of 0.7%. It is believed that an effective amount of the nickel required in the steel is as high as, for example, 0.30-0.70%, more preferably about 0.5%. In a preferred embodiment of the invention, if it is believed that steel in the absence of nickel has sufficient ductility / toughness, for reasons of cost, the steel should not contain nickel in amounts exceeding that which is inevitably contained in steel in the form of nickel impurities to raw materials, i.e. e. contain less than 0.30%.

Further, the steel itself may possibly be alloyed with small amounts of other elements to improve the various properties of the steel, such as hardenability, or to facilitate its production. For example, it is possible to alloy steel with boron in an amount of up to about 30 million hours to increase the ductility of steel in a hot state.

On the other hand, other elements are clearly not required. So, steel does not contain any other, except vanadium, strong carbide-forming elements. Niobium, titanium and zirconium, for example, are clearly not required. Their carbides are more stable than vanadium carbide, and their dissolution during the quenching operation requires a higher temperature than in the case of vanadium carbide. Thus, vanadium carbides begin to dissolve at 1000 ° C and practically completely dissolve at 1100 ° C, and niobium carbides do not begin to dissolve up to a temperature of approximately 1050 ° C. Titanium carbides and zirconium carbides are even more stable and do not begin to dissolve until they reach temperatures above 1200 ° C, while they do not completely dissolve until the molten state of the steel. Strong carbide and nitride forming elements other than vanadium, in particular titanium, zirconium and niobium, should therefore not be present in steel in an amount of more than 0.1%, preferably a maximum of 0.03%, more preferably a maximum of 0.010%. Most preferably, the steel contains a maximum of 0.005% of each of these elements. Also, the content of phosphorus, sulfur, nitrogen and oxygen in the steel is kept very low in order to maximize the ductility and toughness of the steel. Thus, phosphorus may be present as an inevitable impurity in a maximum amount of 0.035%, preferably a maximum of 0.015%, more preferably a maximum of 0.010%. Oxygen may be present in a maximum amount of 0.0020% (20 ppm), preferably a maximum of 0.0015% (15 ppm), more preferably a maximum of 0.0010% (10 ppm). Nitrogen may be present in a maximum amount of 0.030%, preferably a maximum of 0.015%, more preferably a maximum of 0.010%.

If the steel is not sulfonated to increase its workability, the steel contains a maximum of 0.03% sulfur, preferably a maximum of 0.010% S, more preferably a maximum of 0.003% (30 ppm) sulfur. However, it is possible to improve the workability of steel by intentionally adding sulfur in an amount in excess of 0.03%, preferably in excess of 0.10%, but a maximum of 0.30% sulfur. If the steel is sulfonated, it can itself, as is known, also contain 5-75 million parts of Ca and 50-100 million parts of oxygen, preferably 5-50 million parts of Ca and 60-90 million parts of oxygen.

In the manufacture of steel, ingots or billets are obtained, weighing more than 100 kg, preferably up to 10 tons, and a thickness exceeding about 200 mm, preferably at least 300 or 350 mm. Preferably, in conventional metallurgical production, ingots are obtained by melt casting, more preferably siphon casting. Continuous casting can also be carried out provided that it is followed by remelting to the required size specified above, for example by electroslag remelting (ESR). Powder metallurgy and spray stamping are extremely costly methods and offer no cost advantages. The obtained ingots are processed hot in the required size, while the cast structure is also destroyed.

The structure of the material processed in the hot state can be normalized in various ways by heat treatment in order to optimize the homogeneity of the material, for example by homogenization at high temperature, preferably at 1200-1300 ° C. The manufacturer typically delivers the steel to the consumer in a state after softening annealing with a hardness of approximately 200-230 Brinell, typically a hardness of 210-220 Brinell. Tools are usually made by machining steel subjected to soft annealing, but it is also possible, among other things, to make tools by traditional machining or electric spark treatment of hardened and tempered steel.

The heat treatment of the manufactured tools is usually carried out by the consumer, preferably in a vacuum oven, quenching from a temperature between 950-110 ° C, more preferably at 1020-1050 ° C, to completely dissolve the carbides present within 15 minutes to 2 hours, preferably within 15 -60 minutes, followed by cooling to 20-70 ° C and high-temperature tempering at 500-600 ° C, more preferably at 520-560 ° C.

In the state after softening annealing, the steel has a ferritic base consisting of uniformly distributed small carbides, the type of which can be different. In the quenched and tempered state, the steel has a martensite base. Known theoretical calculation methods calculated that the steel in equilibrium contains approximately 0.6% MS-carbides. During high temperature tempering, additional deposition of MS carbides is achieved, which gives the steel the required hardness. These carbides are less than microns in size. Therefore, the amount of these carbides cannot be determined by standard microscopy. With an excessive temperature increase, MS carbides become larger and more unstable, which contributes to the formation of rapidly growing chromium carbides, which is undesirable. For this reason, in the case of the composition of the steel corresponding to the composition according to the invention, it is important to carry out tempering at the above temperature and withstand the required time.

Additional features and aspects of the invention will become apparent from the attached claims and the subsequent description of the experiments, as well as from the accompanying drawings.

Brief Description of the Drawings

In the description of the experiments made links to the accompanying drawings, in which:

Figure 1-Figure 5 relate to studies of steels obtained on a laboratory scale.

Figure 1 shows the dependencies illustrating the effect of tempering temperature on the studied steel.

Figure 2 illustrates the hardenability of the studied steels.

Figure 3 illustrates the ductility, calculated in units of the toughness of the studied materials, depending on the hardness of the samples hardened in a vacuum furnace at different cooling times.

Figure 4 shows a histogram showing the ductility and hardness of the studied steels after specific heat treatment.

Figure 5 shows a histogram showing the hot ductility of the studied steels, respectively, in the cast and forged steel condition.

Fig.6 and Fig.7 relate to studies of steels produced on an industrial scale, and Fig.6 illustrates the ductility of the samples of the studied steels taken in various places of the manufactured rods, and Fig.7 shows the microstructure of the steel according to the invention after heat treatment.

Test Description

Laboratory scale tests

Materials

Four steel alloys were manufactured in the form of laboratory ingots weighing 50 kg. The chemical composition is shown in table 1. Due to the restrictions imposed by production, the sulfur content could not be maintained at the required level. The oxygen content and impurities, in addition to those indicated in the table, were not determined. The following process steps were used: homogenization for 10 hours in air at 1270 ° C, forging to a size of 60 × 60 mm, regeneration treatment at 1050 ° C / 2 h / air, softening annealing at 850 ° C / 2 h, cooling at 10 ° C / h to 600 ° C and then natural cooling in air.

Table 1
The chemical composition of materials manufactured on a laboratory scale, in wt.% Steel FROM Si Mn R S Cr Mo V Ti (million h) Nb (million h) O N (million h) The remainder one 0.68 0.87 0.65 0.005 0.006 2.82 2,34 0.52 33 <10 On. fourteen Fe + impurities 2 0.68 0.19 0.39 0.004 0.006 4.93 2,37 0.37 29th <10 On. 28 Fe + impurities 3 0.71 0.90 0.49 0.004 0.006 5.09 2,36 0.56 39 <10 On. 19 Fe + impurities four 0.63 1.38 0.35 0.007 0.006 4.25 2.87 1.81 42 <10 On. eighteen Fe + impurities On. - not analyzed Table 8
The chemical composition of materials manufactured on an industrial scale, in wt.% (S, B and O in million hours), the remainder is Fe and impurities Steel FROM Si Mn R S Cr Ni Mo W With V Ti Mb Cu Al N AT O 10 0.71 0.19 0.49 0.009 6 4.96 0,07 2.28 0.003 0.010 0.50 0.0016 0.001 0,062 0.017 0.011 10 7 eleven 0.71 0.19 0.49 0.009 8 4.98 0,07 2,30 0.003 0.011 0.50 0.0015 0.001 0,032 0.015 0.011 10 5 12 0.74 0.99 0.76 0.007 10 2,55 0.06 2.09 0.01 0.01 0.50 0.003 0.01 0,07 0,037 0.007 thirty 8

The above materials were investigated in order to compare their hardness after soft annealing, microstructure after various types of heat treatment, hardness after hardening and tempering, hardenability, impact strength, wear resistance and hot ductility. These studies are described below. In addition, theoretical equilibrium calculations were carried out according to the method of thermodynamic calculation (Thermo-Calc) to assess the content of dissolved carbon and carbide fraction at the indicated temperature for steels, the target composition of which is given in table 2.

table 2
The chemical composition of thermodynamically studied alloys, in wt.% Steel FROM Si Mn R S Cr Mo V 5 0.72 1.00 0.75 0.02 0.005 2.60 2.25 0.50 6 0.71 0.20 0.50 0.02 0.005 5.00 2,30 0.55 7 0.74 1.00 0.50 0.02 0.005 5.00 2,30 0.55 8 0.65 1,50 0.40 0.02 0.005 4.20 2.80 1.80

The dissolved carbon content at the autenization temperature, T _A , and the volumetric content (vol.%) Of MS at T _A are shown in Table 3 below.

Table 3 T _A (° C) % C at T _A vol.% MS at T _A 5 1050/30 min 0.63 1.01 6 1050/30 min 0.65 0.72 7 1050/30 min 0.64 1,04 8 1150/10 min 0.38 2.87

Hardness after soft annealing

The hardness after soft annealing, the Brinell hardness (TB) of the studied alloys 1-4 are shown in table 4.

Table 4
Hardness after soft annealing Steel Hardness (TB) one 218 2 208 3 217 four 222

Microstructure

The microstructure was investigated in a softening annealing state after heat treatment to a hardness of 60-61 on the Rockwell C scale. These studies indicate that the microstructure in the quenched and tempered state consists of tempering martensite. Primary carbides were found only in steel 4. These carbides are of the MS type. In none of the alloys were titanium carbides, nitrides and / or carbonitrides found.

Quenching and vacation

Steel 1-3 was austenitized at 1050 ° C / 30 min, and steel 4 was austenitized at 1150 ° C / 10 min, cooled in air to ambient temperature and annealed twice for 2 hours at various tempering temperatures. The effect of tempering temperature on hardness is shown in FIG. It can be seen that steels 2 and 3 can, in principle, be given the required hardness after high temperature tempering at 500-600 ° C, preferably at 520-560 ° C, more preferably at 520-540 ° C. In the case of steels 2 and 3, optimum values from the point of view of maximum hardness are achieved by tempering at a temperature of approximately 525 ° C. This is especially important for steels designed for dies, since nitriding or surface coating at temperatures of the order of 500 ° C or higher is required to obtain the necessary wear resistance for certain tools. At these temperatures, significant secondary hardening is thus achieved due to the precipitation of MS carbides. From the graph shown in Figure 1, it follows that a hardness of more than 60 on the Rockwell scale C is provided by tempering even at approximately 580 ° C, which is an advantage because it allows the application of a surface coating in a sufficiently wide temperature range and there is no significant reduction tool hardness. If higher hardness is required, more carbon and a carbide forming element should be added to the alloy. This, however, can lead to the risk of the formation of primary carbides, which cannot be dissolved during annealing. The above is illustrated by the example of steel 4, which requires a very high austenitization temperature, which has a number of drawbacks - the implementation of the requirements of non-standard technology of hardening by the tool manufacturer, hardening stress, resizing and the possibility of cracking.

Hardenability

A comparison of the hardenability of the studied alloys 1-4 is shown in Figure 2 by plotting data from thermokinetic diagrams (CCT-diagrams). From this graph it is obvious that steel No. 2 has the best hardenability, however, compared to steel No. 1 and especially compared to steel No. 4, steel No. 3 also has better conditions for the formation of martensite during slow cooling of the steel from the austenization temperature.

Plastic

Figure 3 shows the plasticity in terms of the absorbed impact energy in the case of non-notched test rods at 20 ° C, quenched in a vacuum furnace at different cooling times and tempered to different hardness. The highest toughness with a hardness of over 60 on the Rockwell C scale was obtained for steel No. 2, however, this effect is even more noticeable when the hardness exceeds 61 on the Rockwell C scale. For further analysis of the impact strength at the specified hardness of steel 1-4 are also compared on the histogram shown in Figure 4. In this case, steels 1-4 were cooled from the above austenitization temperature for 706 seconds from 800 to 500 ° C and after cooling to room temperature was continued, the steels were tempered at 525-540 ° C / 2 × 2 hours. From FIG. 4 it follows that the highest toughness (under the condition of comparable hardness) is realized in steel 2.

Hot ductility

Among other characteristics, the hot ductility parameter is important in the production of steel from an economic point of view. Hot ductility studies are carried out after homogenization for 10 hours at 1270 ° C / air in cast and forged steel, respectively. In the forged state, regeneration treatment at 1050 ° С / 2 hours and softening annealing were also used. The exposure time at the research temperature was 4 minutes, with the exception of steels 1 and 3 in the cast state, and at a temperature equal to or higher than 1200 ° C for forged materials. The reason for this was that these two steels were significantly oxidized, which prevented the correct measurement of the compression region. Low silicon steel 2, on the other hand, did not significantly oxidize. This steel also had higher ductility in the hot state than steel 1 and 3 in the cast state, as well as in the forged state. For steel 2, a test temperature of approximately 50 ° C is permissible. The results are shown in Fig.5.

Abrasive wear

Wear resistance was investigated in the form of a pin-against-disc test using SiO ₂ as an abrasive agent. Steel 4 showed the highest wear resistance. Other steel alloys were equally good.

The discussion of the results

The above results were used for a comparative study of the studied steels. Table 5 shows the content of dissolved carbon (wt.%) And the content of MS-carbides (vol.%) At 1050 ° С under the assumption that under these conditions, an equilibrium state is reached in the case of steels 1-3 and 5-7, and at 1150 ° С in the case of steels 4 and 8. The data for the target compositions of steels 5-8 are shown in the table for comparison. It can be seen that steel 2 has a significantly lower MS content than their planned amount, since the vanadium content is lower than in the nominal steel composition, i.e. steel 6 containing 0.65 vol.% MS at T _A.

Table 5
The content of dissolved carbon (wt.%) And carbon fraction (vol.%) At the specified austenitization temperature in the case of the studied alloys 1-4 in comparison with the target compositions of 5-8 of these alloys Steel Optimal T _A (° C) % C at T _A % MS at T _A 5 1050/30 min 0.64 0.89 one 1050/30 min 0.60 0.87 6 1050/30 min 0.65 0.65 2 1050/30 min 0.66 0.32 7 1050/30 min 0.65 0.97 3 1050/30 min 0.63 0.95 8 1150/30 min 0.37 2.83 four 1150/30 min 0.30 2.71

A comparison of the properties of the studied alloys 1–4 is given in Table 6. In this table, the grades are assigned grades ranging from 1 to 4, where 1 is the lowest grade and 4 is the highest grade.

Table 6
Comparison of the properties of the studied alloys Steel No. one 2 3 four Hardenability 2 four 3 one Dimensional stability during heat treatment 2 four 3 one Hardness after high temperature hardening four four four 4 ^* Ductility / impact strength 2 four 3 one Wear resistance 2 2 2 four Fatigue Resource four four four 2 Compressive strength four four four four Grindability four four four 2 Machinability four 3 four 2 Spark machinability four four four four Polishability four four four 3 Production Savings 3 four four ^* - however, only after quenching from high temperature

From table 6 it follows that steel No. 2 has a better combination of properties compared with other investigated and evaluated materials. In particular, this steel is better in terms of the most important properties of the product. Possibly, a lower content of MS carbides is unfavorable for steel 2, since this can reduce the resistance to grain growth. Thus, the experience of testing showed that the content of vanadium should be increased from the nominal 0.40 to 0.50% in order to increase the ability to withstand grain growth during heat treatment. The experiments also show that with respect to the toughness of steel for vanadium content, there is a narrow range in which the required resistance to grain growth is provided without leading to a too high carbide content, and also to provide Rockwell hardness 60-62 on the Rockwell C scale after thermal carbon content should be increased nominally to 0.72% and maintained at this value within a fairly narrow range. The content of P, S, N and O should be kept very low in order to optimize ductility and toughness. Other carbide and nitride forming elements, such as Ti, Zr and Mb, should preferably be limited to a maximum of 0.005%. In accordance with this condition, the steel for cold working according to the invention must have a nominal composition shown in table 7.

Table 7
The nominal composition (% wt.) Of the steel of the invention, i.e. steel No. 9, and the amount of dissolved carbon and the amount of carbides (% vol.) at 1050 ° C. FROM Si Mn R S Cr Mo V N ABOUT FROM ^* MS ^* 0.72 0.20 0.50 ≤0.010 0.0010 5,0 2,30 0.50 0.010 0.0010 0.67 0.6 The remainder is iron and inevitable impurities. ^* Calculated theoretically at equilibrium according to the method of thermodynamic calculations (Thermo-Calc method).

Industrial scale experiments

65-ton industrial smelting was carried out in an electric arc furnace, and the target composition of the smelting corresponded to steel No. 9 according to table 7. A number of ingots were made from molten metal, and these ingots were forged into bars of various sizes, including bars with a diameter of 330 mm and 254 mm, respectively steels No. 10 and No. 11 in table 8. The same table shows the chemical composition of the comparison material - steel No. 12. This material was in the form of a forged bar with a diameter of 330 mm. In table 8, not only sulfur and phosphorus are impurities. As impurities, there are some amounts of tungsten, cobalt, titanium, niobium, copper, aluminum, nitrogen and oxygen. Other impurities are not indicated, since their amount is below the permissible level. The remainder is iron.

Test rods were selected from manufactured rods. Figure 7 shows the microstructure of steel, where a sample is taken from the central part of a bar made of steel No. 11. The sample was quenched by austenization at 1025 ° С / 30 min, cooled in air, and then annealed at 525 ° С / 2 × 2 h. It follows from the drawing that the steel had a uniform microstructure consisting of tempering martensite without primary carbides.

The ductility was investigated by means of an impact test carried out on non-notched samples taken respectively from the most critical locations of the rods and in the most critical directions. The test rods of steel No. 10 and No. 11 were quenched to a hardness of 61.0 and 60.5, respectively, on the Rockwell scale C (Rockwell hardness) by austenization at 1025 ° C / 30 min, cooling in air and subsequent annealing at 525 ° C / 2 × 2 h. Samples of steel No. 12 were quenched to a hardness of 60.2 on the Rockwell scale C by austenization at 1050 ° C / 30 min, cooling in air and subsequent annealing at 550 ° C / 2 × 2 h. Absorbed impact energies are given on the histogram of Fig.6. The designations used in the diagram are ИС1 and ИС2 mean:

IS1 is the designation of the test rod obtained from a round bar by selecting from the surface of the bar in its longitudinal direction, and with the direction of impact in the end direction (square direction) of the bar (conditions following the most unfavorable);

IS2 is the designation of the test rod obtained from a round bar and taken from the center of the bar, while other conditions correspond to IS1 (the most unfavorable conditions).

From Fig.6 it follows that the steel according to the invention has a significantly higher ductility compared with the comparison material in case of equality or even slight superiority of hardness values for the steels according to the invention and the comparison material; however, the results were obtained by comparing the impact tests performed on uncut specimens, hardened and tempered, and made of steel produced on an industrial scale.

Claims (33)

1. Steel for cold working, essentially not containing primary carbides and having after quenching and high temperature tempering at 500-600 ° C hardness from 57 to 63 on the Rockwell scale C of the following chemical composition, wt.%: 0.60-0.85 C from trace amounts to 0.3 (Si + Al) 0.1-2.0 Mn 4,5-5,5 Cr 1.5-2.6 Mo, maximum 1.0 W 0.42-0.65 V maximum 0.1 of each of Nb, Ti and Zr maximum 2.0 Co iron and unavoidable impurities are the rest. 2. Steel for cold working according to claim 1, characterized in that it contains at least 0.63 wt.%, Preferably at least 0.68 wt.% C. 3. Steel for cold working according to claim 2, characterized in that it contains a maximum of 0.8 wt.%, Preferably a maximum of 0.78 wt.% C. 4. Steel for cold working according to claim 1, characterized in that it contains a maximum of 0.6 wt.%, Preferably a maximum of 0.55 wt.% V. 5. Steel for cold working according to claim 1, characterized in that it contains approximately 0.72 wt.% C and approximately 0.50 wt.% V. 6. Steel for cold working according to claim 1, characterized in that it contains at least 0.05 wt.% Si. 7. Steel for cold working according to claim 6, characterized in that it contains at least 0.1 wt.%, Preferably at least 0.2 wt.% Si. 8. Steel for cold working according to claim 1, characterized in that it contains a maximum of 0.1 wt.% And preferably a maximum of 0.03 wt.% Al. 9. Steel for cold working according to claim 1, characterized in that it contains at least 1.8 wt.% Mo. 10. Steel for cold working according to claim 9, characterized in that it contains at least 2.1 wt.% Mo. 11. Steel for cold working according to claim 9, characterized in that it contains a maximum of 0.3 wt.%, Preferably a maximum of 0.1 wt.% W. 12. Steel for cold working according to claim 11, characterized in that the amount of tungsten contained therein does not exceed an impurity level. 13. Steel for cold working according to claim 1, characterized in that it contains a maximum of 0.7 wt.% Co. 14. Steel for cold working according to item 13, wherein the amount of cobalt contained therein does not exceed the impurity level. 15. Steel for cold working according to claim 1, characterized in that the content in it of each of such elements as titanium, zirconium and niobium does not exceed 0.1 wt.%. 16. Steel for cold working according to claim 1, characterized in that it further comprises a maximum of 2.0 wt.% Ni. 17. Steel for cold working according to claim 1, characterized in that it further comprises a maximum of 1.0 wt.% Ni. 18. Steel for cold working according to 17, characterized in that it further comprises a maximum of 0.7 wt.% Ni. 19. Steel for cold working according to claim 18, characterized in that the amount of nickel contained therein does not exceed an impurity level. 20. Steel for cold working according to clause 15, characterized in that the content in it of each of such elements as titanium, zirconium and niobium does not exceed 0.03 wt.%. 21. Steel for cold working according to claim 20, characterized in that the content in each of such elements as titanium, zirconium and niobium does not exceed 0.01 wt.%, Preferably does not exceed 0.005 wt.%. 22. Steel for cold working according to claim 1, characterized in that it contains a maximum of 0.035 wt.%, Preferably a maximum of 0.015 wt.%, And more preferably a maximum of 0.010 wt.% R. 23. Steel for cold working according to claim 1, characterized in that it contains a maximum of 20, preferably a maximum of 10 million hours ABOUT. 24. Steel for cold working according to claim 1, characterized in that it contains a maximum of 0.03 wt.%, Preferably a maximum of 0.015 wt.% And more preferably a maximum of 0.010 wt.% N. 25. Steel for cold working according to claim 1, characterized in that it contains a maximum of 0.03 wt.%, Preferably a maximum of 0.01 wt.% And more preferably a maximum of 30 million hours S. 26. Steel for cold working according to claim 1, characterized in that it contains from 0.10 to 0.3 wt.% S. 27. Steel for cold working according to p. 26, characterized in that it contains from 5 to 75 million hours Ca and from 50 to 100 million hours About, preferably from 5 to 50 million hours Ca and preferably from 60 to 90 million hours ABOUT. 28. Steel for cold working according to any one of claims 1 to 27, characterized in that after quenching and high-temperature tempering at 500-600 ° C, preferably at 520-560 ° C, its hardness is from 57 to 63 on the Rockwell scale C preferably 60 to 62 on the Rockwell C scale. 29. Steel for cold working according to p. 28, characterized in that after quenching and high temperature tempering at 500-600 ° C, its hardness is from 57 to 63 on the Rockwell scale C, preferably from 60 to 62 on the Rockwell scale C. 30. A tool for cold working made of steel for cold working according to any one of claims 1 to 29. 31. The tool for cold working according to claim 30, characterized in that after quenching and high temperature tempering at 500-600 ° C, preferably at 520-560 ° C, its hardness is from 57 to 63 on the Rockwell scale C, preferably from 60 up to 62 on the Rockwell C scale. Priority on points: 06/13/2002 according to claims 1-15, 20-29; 01/29/2003 according to claims 16-19, 30-31.

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